Ceramic molds for manufacturing metal casting and methods of manufacturing thereof

ABSTRACT

Disclosed herein is a method comprising disposing a gel casting composition between an outer die and a wax pattern; wherein the wax pattern is a replica of a desired casting; reacting the gel casting composition to form a gel matrix; removing the wax pattern; extracting a solvent from the gel matrix to form a dried gel; and firing the dried gel to form a gel cast mold. Disclosed herein too is a method comprising disposing a gel casting composition between an outer die and a wax pattern; wherein the wax pattern is a replica of a turbine component; reacting the gel casting composition to form a gel matrix; removing the wax pattern; extracting a solvent from the gel matrix to form a dried gel; and firing the dried gel to form a gel cast mold.

BACKGROUND

This disclosure relates to ceramic molds and methods for manufacturing ceramic molds. In particular, this disclosure relates to ceramic molds for manufacturing turbine metal castings.

Ceramic molds made from currently available techniques suffer from a variety of failures that can be attributed to the method of manufacturing the molds. For conventional slip-casting, one particular drawback is the inability to dry molds along the inner surface. This leads to cracking of the molds during casting. In order to overcome this problem, molds are generally built layer by layer. While this overcomes the problem with drying, it leads to heterogeneity problems within the mold. One example of heterogeneity that occurs as a result of building the mold layer by layer is the difference in coefficient of thermal expansion between the various layers. This can lead to delamination and cracking of the mold. In addition, the method of manufacturing molds by applying layer upon layer gives rise to problems when wall thickness of less than or equal to about 1 mm are desired. Furthermore, by constructing the mold layer-by-layer, the mold is generally of uniform thickness throughout, which is sometimes undesirable.

It is therefore desirable to build molds that can survive molding procedures at elevated temperatures while maintaining the flexibility of design normally associated with conventional slip-cast molds.

SUMMARY

Disclosed herein is a method comprising disposing a gel casting composition between an outer die and a wax pattern; wherein the wax pattern is a replica of a desired casting; reacting the gel casting composition to form a gel matrix; removing the wax pattern; extracting a solvent to form a dried gel; and firing the dried gel to form a gel cast mold.

Also disclosed herein is a method comprising disposing a gel casting composition between an outer die and a wax pattern; wherein the wax pattern is a replica of a turbine component; reacting the gel casting composition to form a gel matrix; removing the wax pattern; extracting a solvent from the gel matrix to form a dried gel; and firing the dried gel to form a gel cast mold.

DETAILED DESCRIPTION OF FIGURES

FIG. 1 is a schematic depicting a system 10 comprising a wax pattern 2, an outer die 4, and a gel casting composition 6 disposed therebetween; and

FIG. 2 is a schematic depicting the process steps for manufacturing a mold that can be used for molding metal castings.

DETAILED DESCRIPTION

Disclosed herein are methods for manufacturing molds that can be used for molding metal castings. In an exemplary embodiment, the molds can be used for manufacturing turbine parts. In one method of manufacturing the molds, a gel casting composition can be cast around a wax pattern. The wax pattern is a replica of a desired metal casting. An outer die is used to form the outer surface of the mold. The gel casting composition is poured into the space between the wax pattern and the outer die. In one embodiment, after the gel casting composition solidifies into a gel matrix, it is removed from the die and dried. The wax pattern may be removed from the gel matrix by melting and pouring the wax from the mold. The wax pattern may also be removed by abrading, etching or dissolving it.

With reference now to FIG. 1, a system 10 for molding metal casting comprises an outer die 4 into which a gel casting composition 6 is poured. A wax pattern 2, which is a replica of a desired casting is then placed into the gel casting composition 6 in the outer die 4. Upon polymerizing the gel casting composition to form a solidified gel matrix, the wax pattern 2 is removed. The gel matrix is then removed from the outer die 4 and dried to form a dried gel. The dried gel is then fired at temperatures of greater than or equal to about 300° C. to form a gel cast mold.

This method is advantageous in that the wall thickness of the mold can be controlled. Another advantage is that the mold can be engineered to maximize strength, thereby reducing mold failures. Manufacturing a mold by gel casting also reduces the time required for making a mold, thereby improving productivity and reducing costs.

In one embodiment a gel casting composition comprises an inorganic powder, a monomer, a solvent, and other desired additives. The inorganic powder can be metallic or ceramic. Examples of suitable metal powders include steels, aluminum alloys, superalloys, titanium alloys, copper alloys, or a combination comprising at least one of the aforementioned metal powders. Examples of ceramic powders include alumina, silica, zirconia, magnesia, chromium oxide, iron oxide, zinc oxide, hydroxylapatite, silicon nitride, silicon carbide, boron nitride, refractory carbides (such as titanium carbide (TiC), tantalum carbide (TaC), or the like), refractory nitrides (such as titanium nitride (TiN), tantalum nitride (TaN), tungsten nitride (WN), or the like), refractory borides (such as titanium diboride (TiB₂), zirconium diboride (ZrB₂), or the like), clays, spinels, mullite, ferrites, titanates, zircon, glass frits, or a combination comprising at least one of the aforementioned materials.

In one embodiment, the metal or ceramic powder can have micrometer sized or nanometer sized (hereinafter nanosized) particles. Micrometer sized particles generally have particle sizes greater than or equal to about 1.2 micrometers (μm). In one embodiment, the micrometer sized particles have particle sizes greater than or equal to about 1.5 μm. In another embodiment, the micrometer sized particles have particle sizes greater than or equal to about 1.8 μm. In yet another embodiment, the micrometer sized particles have particle sizes greater than or equal to about 2.5 μm. In yet another embodiment, the micrometer sized particles have particle sizes greater than or equal to about 5.0 μm.

Exemplary nanosized particles include metal oxides, highly crosslinked silicones, polyhedral oligomeric silsesquioxanes (POSS) macromers, metal carbides, nanoclays and the like, which have maximum particle sizes less than or equal to about 1200 nm. In general it is desirable to use nanosized particles wherein the particle sizes are less than or equal to about 500, preferably less than or equal to about 200, preferably less than or equal to about 100, and more preferably less than or equal to about 40 nanometers.

Nanosized metal oxides that may be used in the compositions are metal oxides of alkali earth metals, alkaline earth metals, transition metals and other commonly used metals. Suitable examples of metal oxides are calcium oxide, cerium oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, copper oxide, aluminum oxide, or the like, or combinations comprising at least one of the aforementioned metal oxides. Nanosized metal carbides such as silicon carbide, titanium carbide, tungsten carbide, iron carbide, or the like, or combinations comprising at least one of the aforementioned metal carbides may also be used in the compositions. The metal oxides and carbides are generally particles having surface areas in an amount of about 1 to about 1000 m²/gm. Within this range it is generally desirable for the metal oxides and carbides to have surface areas greater than or equal to about 5 square meter/gram (m²/gm), preferably greater than or equal to about 10 m²/gm, and more preferably greater than or equal to about 15 m²/gm. Also desirable within this range is a surface area less than or equal to about 950 m²/gm, preferably less than or equal to about 900 m²/gm, and more preferably less than or equal to about 875 m²/gm.

Commercially available examples of nanosized metal oxides are NANOACTIVE™ calcium oxide, NANOACTIVE™ calcium oxide plus, NANOACTIVE™ cerium oxide, NANOACTIVE™ magnesium oxide, NANOACTIVE™ magnesium oxide plus, NANOACTIVE™ titanium oxide, NANOACTIVE™ zinc oxide, NANOACTIVE™ silicon oxide, NANOACTIVE™ copper oxide, NANOACTIVE™ aluminum oxide, NANOACTIVE™ aluminum oxide plus, all commercially available from NanoScale Materials Incorporated. Commercially available examples of nanosized metal carbides are titanium carbonitride, silicon carbide, silicon carbide-silicon nitride, and tungsten carbide all commercially available from Pred Materials International Incorporated.

The gel casting composition comprises the ceramic or metal powder in an amount of 10 to about 95 weight percent (wt %), based upon the weight of the gel casting composition. In one embodiment, the gel casting composition comprises the ceramic or metal powder in an amount of 20 to about 85 wt % based upon the weight of the gel casting composition. In another embodiment, the gel casting composition comprises the ceramic or metal powder in an amount of 30 to about 75 wt % based upon the weight of the gel casting composition. Commercially available ceramic powders (e.g., whitewares, alumina, mullite, zircon, silicon nitride, silicon carbide) can be used in an amount of about 40 to about 90 wt %, based upon the weight of the gel casting composition.

The monomer is generally used in the gel casting composition to form a slurry mixture. The monomer may be used in conjunction with a solvent to form a monomer solution. The monomer solution provides a low viscosity vehicle for the inorganic powder. Additionally, when heated, the monomer solution polymerizes and gels to form a firm, strong polymer/solvent gel matrix. The gel matrix immobilizes the inorganic in the desired shape of the mold in which the slurry mixture is heated.

In one embodiment, exemplary monomers are those that have vinyl or allyl functionalities. Examples of suitable monomers are acrylic acid, methacrylamide, methacrylic acid, methoxy (polyethylene glycol) monomethacrylate, n-vinyl pyrrolidone, acrylamide, alkyl-acrylamides, alkyl-methacrylamides, alkyl-acrylates, alkyl-methacrylates, dimethyl aminoethyl methacrylate, dimethyl aminopropyl methacrylamide, hydroxy-alkyl acrylamides, hydroxy-alkyl methacrylamides, hydroxy-alkyl acrylates, hydroxy-alkyl methacrylates, methacrylatoethyl trimethyl ammonium chloride, methacrylamidopropyl trimethyl ammonium chloride, p-styrene sulfonic acid, p-styrene sulfonic acid salts, or a combination comprising at least one of the aforementioned monomers.

An exemplary acrylamide is hydroxymethylacrylamide, n-metholoylacrylamide (HMAM). Another exemplary acrylamide is N,N′-methylenebisacrylamide (MBAM).

In another embodiment, exemplary monomers for use in the gel casting composition are those that can be reacted to form epoxies, phenol-formaldehydes, epoxy-modified novolacs, furans, urea-aldehydes, melamine-aldehydes, polyester resins, alkyd resins, phenol formaldehyde novolacs, phenol formaldehyde resoles, phenol-aldehydes, resole and novolac resins, epoxy modified phenolics, polyacetals, polysiloxanes, polyurethanes, or a combination comprising at least one of the foregoing.

In one embodiment, the monomers used in the gel casting composition can be used to form cold setting resins. Cold setting resins are those that can react at room temperature without the use of additional heat. Cold setting resins generally cure at a temperature of less than or equal to about 65° C. Thus, for example, a thermosetting polymer that cures at 80° C. is not a cold setting resin. Examples of suitable cold setting resins include epoxies cured with an amine when used alone or with a polyurethane, alkaline modified resoles set by esters (e.g., ALPHASET® and BETASET®), furans, e.g., furfuryl alcohol-formaldehyde, urea-formaldehyde, and free methylol-containing melamines set with acid. For the purposes of this description, a cold set resin is any resin that can normally be cured at room temperature.

The monomers used in the gel casting composition may be used in an amount of 1 to about 40 wt %, based on the total weight of the gel casting composition. In one embodiment, the monomers used in the gel casting composition may be used in an amount of 2 to about 30 wt %, based on the total weight of the gel casting composition. In another embodiment, the monomers used in the gel casting composition may be used in an amount of 3 to about 20 wt %, based on the total weight of the gel casting composition.

Thermoplastic polymers may optionally be used in the gel casting composition. While it is generally desirable for thermoplastic polymers to be used in the gel casting composition to have glass transition temperatures (Tg's) that are less than or equal to about 50° C., thermoplastic polymers having Tg's greater than or equal to about 50° C. may be used depending upon the solvents employed in the gel casting composition. Exemplary polymers having Tg's less than or equal to about 50° C., are polyalkylene glycols and polyacrylamides. Examples of suitable polyalkylene glycols are polytetramethylene oxide, polyethylene glycol, or the like, or a combination comprising at least one of the aforementioned polyalkylene glycols. Other thermoplastic polymers having glass transition temperatures below 50° C. that may be used in the gel casting composition are thermoplastic elastomers. Examples of suitable thermoplastic elastomers are ionomers, block copolymers, or a combination comprising at least one of the aforementioned thermoplastic elastomers. An exemplary commercially available thermoplastic ionomers is SURLYN® manufactured by Du Pont. An exemplary thermoplastic block copolymer is a styrene butadiene rubber (SBR) comprising a diblock or triblock copolymer.

Thermoplastic polymers that have Tg's above 50° C., that may be used in the gel casting solution are polyethylene terephthalate, polyvinyl alcohol, polymethylmethacrylate, polystyrene, polycarbonate, polyvinyl chloride, cellulose, a cellulose derivative, polyacrylic acid, or the like, or a combination comprising at least one of the aforementioned thermoplastic polymers.

Other exemplary polymers that can be added to the gel casting composition are natural polymers. An example of a natural polymer that can be added to the gel casting composition is a polysaccharide. Exemplary polysaccharides are agar, xanthan gum, starch, locust bean gum, or the like, or a combination comprising one of the aforementioned polysaccharides. Moreover, a polymer gel produced from a solution of a natural polymer may include at least one protein, for example, gelatin and albumin.

If a thermoplastic polymer used in the gel casting composition, it may be used in an amount of 1 to about 40 wt %, based on the total weight of the gel casting composition. In one embodiment, the thermoplastic polymer used in the gel casting composition may be used in an amount of 2 to about 30 wt %, based on the total weight of the gel casting composition. In another embodiment, the thermoplastic polymer used in the gel casting composition may be used in an amount of 3 to about 20 wt %, based on the total weight of the gel casting composition.

Solvents may also be added to the gel casting composition as desired. An exemplary solvent is water. Other organic solvents having a polar protic character, polar aprotic character or non-polar character may be used as desired. Solvents can generally be used in amounts of about 1 to about 30 wt %, based on the weight of the gel casting composition. In one embodiment, the solvent may be used in amounts of about 2 to about 20 wt %, based on the weight of the gel casting composition. In another embodiment, the solvent may be used in amounts of about 3 to about 10 wt %, based on the weight of the gel casting composition.

An initiator can be added to the gel casting composition in order to activate polymerization of the monomer. The initiator may be a free-radical initiator. Examples of suitable free-radical initiators include ammonium persulfate, ammonium persulfate and tetramethylethylenediamine mixtures, sodium persulfate, sodium persulfate and tetramethylethylenediamine mixtures, potassium persulfate, potassium persulfate and tetramethylethylenediamine mixtures, azobis[2-(2-imidazolin-2-yl)propane] HCl (AZIP), and azobis(2-amidinopropane) HCl (AZAP), 4,4′-azo-bis-4-cyanopentanoic acid, azobisisobutyramide, azobisisobutyramidine.2HCl, 2-2′-azo-bis-2-(methylcarboxy)propane, 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, or the like, or a combination comprising at least one of the aforementioned free-radical initiators. Some additives or comonomers can also initiate polymerization, in which case a separate initiator may not be desired. The initiator can control the reaction in addition to initiating it. The initiator is used in amounts of about 0.005 wt % and about 0.5 wt %, based on the weight of the gel casting composition.

Other initiator systems, in addition to free-radical initiator systems, can also be used in the gel casting composition. These include ultraviolet (UV), x-ray, gamma.-ray, electron beam, or other forms of radiation, which could serve as suitable polymerization initiators. The initiators may be added to the gel casting composition either during the manufacture of the composition or just prior to casting.

Dispersants, flocculants, and suspending agents can also be optionally added to gel casting composition to control the flow behavior of the composition. Dispersants make the composition flow more readily, flocculants make the composition flow less readily, and suspending agents prevent particles from settling out of composition. These additives are generally used in amounts of about 0.01 to about 10 wt %, based on the total weight of the ceramic or metal powder in the gel casting composition.

Various dispersants for inorganic powders can also be added to the gel casting composition. It is generally desirable for the dispersant not to interact with the initiator. Examples of suitable dispersants include inorganic acids, inorganic bases, organic acids, organic bases, polyacrylic acid, salts of polyacrylic acid, polymethacrylic acid, salts of polymethacrylic acid, copolymers of polyacrylic acid, salts of copolymers of polyacrylic acid, copolymers of polymethacrylic acid, salts of copolymers of polymethacrylic acid, polyethylene imine, polyvinylpyrrolidone, polyacrylamide, lignosulfonates, poly (ethylene oxide), adducts of ethylene oxide, adducts of propylene oxide, polycarboxylates, salts of polycarboxylates, naphthalene sulfonates, sulfosuccinates, polyphosphates, sodium silicates, phosphate esters, or the like, or a combination comprising at least one of the aforementioned dispersants.

Other additives can be included in order to modify the gel properties of the gel casting composition. Examples of suitable additives include plasticizers to modify the mechanical properties of the gel in the wet and dry states, electrolytes, defoamers, bactericides, fungicides, soluble functional polymers, inorganic particles or fibers. Soluble functional polymers are any polymeric species that are added to the gel or to the gel precursor to modify the properties of the gel or the gel precursor. These might include emulsifiers, dispersants, thickeners, polyelectrolytes, chelating agents, foaming agents, suspending agents, or a combination comprising at least one of the aforementioned soluble functional properties.

The level of additive used in a particular gel casting composition can vary widely. It will depend directly on the role that the additive is playing in the gel casting composition. For example, one might add a plasticizer to the monomer solution to provide a more compliant polymer in the gelled and dried state. The plasticizer content would be added on the order of several percent, based on the weight of the dried gel (dried gels are obtained after the gel casting composition is dried). A bactericide can be added to the monomer solution to prevent growth of bacteria during storage. This would be added in parts per million, based on the weight of the gel casting composition. Foam control agents are added to gel casting compositions to either remove bubbles or form bubbles in the composition. Foam control agents are generally added at from about 0.01 to about 2 wt %, based on the weigh of the gel casting composition.

As noted above, molds manufactured from the gel casting composition may be used for molding metal castings. In one exemplary embodiment, the gel cast molds may be used for manufacturing turbine components. These turbine components can be used in either power generation turbines such as gas turbines, hydroelectric generation turbines, steam turbines, or the like, or they may be turbines that are used to facilitate propulsion in aircraft, locomotives, or ships. Examples of turbine components that may be manufactured using gel cast molds are stationary and/or rotating airfoils. Examples of other turbine components that may be manufactured using gel cast molds are seals, shrouds, splitters, or the like.

In one embodiment, in one manner of manufacturing a gel cast mold, the metallic or ceramic powder, the monomer, the solvent, and optional additives may be combined in a suitable manner to form the gel casting composition. FIG. 2 depicts some exemplary steps that may be used to convert a gel casting composition into a gel cast mold. The gel casting composition formed by mixing the ceramic or metallic powder, the monomer and the solvent is generally in the form of a slurry. In an exemplary embodiment, the gel casting composition is formed by dissolving a dispersant in the monomer to form a monomer solution followed by the addition of the inorganic powder and the solvent to the monomer solution. An initiator may be added to the gel casting composition if desired. The resultant gel casting composition is then poured into the space between the die and the wax pattern. As noted above, the wax pattern is a replica of the desired metal casting. The wax casting is placed into the desired position in the die and is held in position until the gel casting composition is poured. After the gel casting composition is formed into a desired shape, it is heated for a temperature and a time sufficient for the monomer and any optional comonomer to polymerize and gel to form a firm gel matrix.

The temperature at which the polymerization occurs depends on the initiator as well as the monomers and/or comonomers that used in the gel casting composition. The polymerization reaction is generally conducted at temperatures between the freezing point and the boiling point of the solvent being used. Heating activates the free-radical initiator, and a temperature of about 50° C. can be used to activate polymerization in many systems. Generally, polymerization temperatures of about 1° C. to about 100° C. are desirable. In one embodiment, the polymerization is conducted at a temperature of about 15° C. to about 80° C.

The gel time to form a firm gel matrix is dependent on the combination of monomers, the weight percent of the metallic or ceramic particles, the solvent and the type of the initiator. In general, it is desirable for the gel casting composition to be heated for a time period of greater than or equal to about 1 minute. In one embodiment, the slurry is heated for a period of from about 1 to about 120 minutes in order to polymerize the monomers and form a firm gel matrix. In another embodiment, the slurry is heated for a period of from about 2 to about 90 minutes in order to polymerize the monomers and form a firm gel matrix.

The gel matrix can be formed under vacuum, or at pressures greater than atmospheric, and as high as about 300 pounds per square inch (psi). The reaction can be carried out at atmospheric pressure, although other pressures can be utilized to produce gel matrices having different properties. After heating, the resultant shaped, solid gel matrix may be cooled to ambient temperature. The gel matrix is in a wet, green condition in that it contains plasticizer and/or solvent and is in the unfired form. The green product may subsequently be heated in order to substantially remove the solvent to provide a dried gel. The specific temperature and time suitable for producing the dried gel depends on the specific metallic or ceramic powder and monomer employed. Initially, drying should be conducted at a temperature such that evaporation is not too rapid. Consequently, the initial drying temperature will generally be closer to the melting point than to the boiling point of the solvent. As the drying process proceeds, the temperature may be raised to provide faster drying rates. In order to drive off the last traces of solvent from the gel matrix, temperatures in excess of the boiling point of water may be used. In general, drying can be conducted for at least one hour to about 30 hours to obtain the dried gel.

The wax pattern may then be removed from the dried gel. In one embodiment, the wax pattern may be removed by melting it. In another embodiment, the wax pattern may be removed by dissolution. In yet another embodiment, the was pattern may be removed by abrasion or etching. The dried gel may then be removed from the die and subjected to firing in order to decompose the polymer formed by the polymerization of monomer. The dried gel after firing will hereinafter be referred to as a gel cast mold.

The firing is generally conducted at a temperature of greater than or equal to about 300° C. During firing, no shrinkage takes place. Consequently, the mold remains about 40% porous. While casting into a formed outer die is preferred for the method of the present invention, other molding techniques, including extrusion molding, or solid free form fabrication may also be employed. Moreover, other additives known in the ceramic processing arts, for example, mold release agents, may be included in the gel casting compositions for their known functions.

As noted above, this method is advantageous in that the wall thickness of the mold can be controlled. Another advantage is that the mold can be designed to maximize strength, thereby reducing mold failures. Manufacturing a mold by gel casting also reduces the time consumed for making a mold, thereby improving production and reducing costs.

In one advantageous embodiment, this method of making castings can be used to manufacture castings having cross-sectional areas less than or equal to about 2 square centimeters (cm²). In one embodiment, cross-sectional areas of less than or equal to about 1 cm² can be manufactured by this method. In another embodiment, cross-sectional areas of less than or equal to about 0.5 cm² can be manufactured by this method.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention. 

1. A method comprising: disposing a gel casting composition between an outer die and a wax pattern; wherein the wax pattern is a replica of a desired casting; reacting the gel casting composition to form a gel matrix; removing the wax pattern; extracting a solvent from the gel matrix to form a dried gel; and firing the dried gel to form a gel cast mold.
 2. The method of claim 1, further comprising using the gel cast mold to mold castings.
 3. The method of claim 1, wherein the wax pattern is a replica of a turbine component.
 4. The method of claim 3, wherein the turbine component is a stationary or rotating airfoil.
 5. The method of claim 3, wherein the turbine component is a seal, a shroud or a splitter.
 6. The method of claim 1, wherein the gel casting composition comprises a monomer, a metal or ceramic powder and a solvent.
 7. The method of claim 6, wherein the monomer comprises acrylic acid, methacrylamide, methacrylic acid, hydroxymethylacrylamide, n-metholoylacrylamide, N,N′-methylenebisacrylamide, methoxy (polyethylene glycol) monomethacrylate, n-vinyl pyrrolidone, acrylamide, alkyl-acrylamide, alkyl-methacrylamide, alkyl-acrylate, alkyl-methacrylate, dimethyl aminoethyl methacrylate, dimethyl aminopropyl methacrylamide, hydroxy-alkyl acrylamide, hydroxy-alkyl methacrylamide, hydroxy-alkyl acrylate, hydroxy-alkyl methacrylate, methacrylatoethyl trimethyl ammonium chloride, methacrylamidopropyl trimethyl ammonium chloride, p-styrene sulfonic acid, p-styrene sulfonic acid salts, or a combination comprising at least one of the aforementioned monomers.
 8. The method of claim 6, wherein the monomer comprises hydroxymethylacrylamide.
 9. The method of claim 6, wherein the metallic or ceramic particles have particle sizes of less than or equal to about 1,200 nanometers.
 10. The method of claim 6, wherein the metallic or ceramic particles have particle sizes greater than 1200 nanometers.
 11. The method of claim 6, wherein the solvent is water.
 12. An article manufactured by the method of claim
 1. 13. A method comprising: disposing a gel casting composition between an outer die and a wax pattern; wherein the wax pattern is a replica of a turbine component; reacting the gel casting composition to form a gel matrix; removing the wax pattern; extracting a solvent from the gel matrix to form a dried gel; and firing the dried gel to form a gel cast mold.
 14. The method of claim 13, wherein removing the wax pattern is accomplished by melting the wax pattern.
 15. The method of claim 13, wherein removing the wax pattern is accomplished by dissolution, abrasion and/or etching.
 16. The method of claim 13, further comprising removing the gel matrix from the outer die.
 17. The method of claim 13, wax pattern is a replica of a stationary or rotating airfoil.
 18. The method of claim 13, wax pattern is a replica of a seal, a shroud or a splitter.
 19. A turbine component manufactured by the method of claim
 13. 